United States
                    Environmental Protection
                    Agency
Water Engineering Research
Laboratory
Cincinnati OH 45268
                    Research and Development
EPA/600/S2-85/102  Nov. 1985
&ER&         Project Summary
                    Organic  Chemical  Fate
                    Prediction  in  Activated  Sludge
                    Treatment Processes
                    J. W. Blackburn, W. L. Troxler, K. N. Truong, R. P. Zink, S. C. Meckstroth, J. R.
                    Florance, A. Groen, G. S. Sayler, R. W. Beck, R. A. Minear, A. Breen, and0. Yagi
                      This project summary describes re-
                    sults from a broadly based effort to
                    determine the feasibility of predicting
                    the fates of organic chemicals in dif-
                    fused air. activated sludge wastewater
                    treatment processes. The three conver-
                    sion/removal mechanisms emphasized
                    in this work were stripping, sorption on
                    biomass, and bio-oxidation (biotransfor-
                    mation  and mineralization). After an
                    initial literature review and  critique,
                    separate projects were implemented to
                    study experimental and mathematical
                    predictive methods on each individual
                    fate mechanism and to develop exper-
                    imental and/or mathematical protocols
                    where needed. Finally, a project was
                    implemented to couple the mechanisms
                    in a semi-deterministic predictive equa-
                    tion and to attempt initial verification
                    for the equation in a continuous, com-
                    pletely  mixed laboratory activated
                    sludge study.
                      Specific compounds  studied  in this
                    project  include  methyl ethyl ketone,
                    toluene, phenol, aniline, 1,4-dichloro-
                    benzene, 2,4-dichlorophenol, and pent-
                    achlorophenol. Only certain compounds
                    typical for the mechanism of interest
                    were studied in each mechanism proj-
                    ect. Both  14C-labeled and  nonlabeled
                    compounds were used in the sorption,
                    bio-oxidation, and laboratory activated
                    sludge projects to provide independent
                    and corroborative analysis as well as an
                    unambiguous measure of bio-oxidation
                    mineralization.
                      Stripping studies in a coarse bubble
                    diffuser reactor determined the kinetic
                    relationships between compound Hen-
                    ry's law constants, liquid volume, and
air flow rate and the effects of contam-
inants on stripping kinetics. Sorption
studies used nonviable biomass in a
special variable-volume reactor to meas-
ure sorption equilibria and to estimate
sorption kinetics. Predictive equations
are proposed for stripping and sorption
processes.
  Bio-oxidation kinetics for both bio-
transformation and mineralization were
determined for batch, fill-and-draw, and
continuous systems. First-and second-
order (first-order in both substrate and
biomass concentrations) kinetics were
formulated. Specific degrader and total
viable subpopulations were enumerat-
ed.
  An  algebraic, coupled, predictive
equation and related fate equations are
proposed for diffused air, completely
mixed activated sludge systems. Unver-
ified examples of the use  of these
equations for fate prediction are also
presented.
  This Project Summary was developed
by EPA's Water Engineering Research
Laboratory, Cincinnati.  OH, to an-
nounce key findings of the research
project that is fully documented in a
separate report of the same  title (see
Project Report ordering information at
back).

Introduction
  The goal of this research was to eval-
uate the potential of developing a method
for quantitatively predicting the fates of
chemicals in an activated sludge plant—a
predictive fate method (PFM).  For PFM
development, the theory behind the spe-
cific transport and  conversion mechan-

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isms must be known and these mechan-
isms must be coupled into a combined,
dynamic model. Experimental data must
exist or be generated on each mechanism
to evaluate and verify the model. Collec-
tion of these data must be controlled so
that the effects of different mechanisms
can be analyzed separately. The model or
method must be extensively tested, ulti-
mately against full-scale data.
  This project  was conceptualized with
the following objectives:
  1.  To survey and assess the existing
     data base related to stripping, bio-
     mass sorption,  and  bio-oxidation
     mechanism  rate predictions.
  2.  To select a limited list of compounds
     for study that might be indicative of
     the behavior of many more organic
     compounds.
  3.  To develop experimental protocols
     to measure and quantify the kinetics
     of stripping, sorption onto biomass,
     and bio-oxidation.
  4.  To develop mathematical protocols
     or models to describe the removal/
     conversion rates for the stripping,
     sorption,and bio-oxidation mechan-
     isms.
  5.  To develop an overall experimental
     protocol for measuring the mechan-
     ism kinetic  rates in a continuous
     system more representative of real
     operating activated sludge  plants.
  6.  To develop an overall mathematical
     protocol or model to incorporate the
     individual mathematical predictors
     and describe compound fates in a
     complex system indicative of an
     operating activated sludge plant.
  7.  To determine the feasibility of eval-
      uating the  kinetic rate  and other
     constants necessary for individual
     or coupled mechanism fate predic-
     tion from  physical,  chemical, or
     structural properties of the com-
     pound itself.
  The literature was surveyed to deter-
mine the present  level of understanding
of the relationships between chemicals
and  their treatment in activated  sludge
treatment processes. Treatability  was
analyzed in terms of the basic removal/
conversion mechanisms of (1) bio-oxida-
tion, (2)  stripping, and (3)  sorption. In
some cases, other mechanisms such as
chemical oxidation, hydrolysis, or photol-
ysis  become  important. The first three
mechanisms were given priority in this
study.
  Selection criteria were developed and
applied to a large list of aromatic com-
                                   2
pounds resulting  in  a  limited  set of
compounds that potentially represented a
wide range of variation in each removal
mechanism.
  Compounds ultimately studied  in this
project are:
• Stripping: toluene,  1,4-dichloroben-
  zene, methyl ethyl ketone, phenol
• Sorption: phenol, 1,4-dichloroben-
  zene, pentachlorophenol
• Bio-oxidation: phenol, toluene, aniline,
  2,4-dichlorophenol (very limited test-
  ing)
• Laboratory scale activated sludge:
  phenol, toluene, aniline, pentachloro-
  phenol (biological rates minimized)
  A waste stream was  selected that
possessed time based  uniformity. Pulp
and  paper mill foul  condensate is a
distillate of the liquor from the pulping
process and is relatively uniform in
composition over time. The focus of this
study  was to determine methods to
predict fates of organic compounds added
to this wastewater, not to determine the
treatability of a  specific industrial waste
stream.
  Biologically inactive (nonviable) biomass
was required for conducting experiments
on the biological sorption of organics.
Five  techniques were tested: gamma
irradiation, formaldehyde treatment, ly-
ophilization, lyophilization followed by dry
heating, and lyophilization followed by
exposure to UV light. Biomass from the
acclimation reactors  was used in all
experiments. Of the' methods tested, the
most desirable was lyophilization of act-
ivated sludge followed by dry heating at
105°C for 3 hours. This method produced
a stable, dry product that upon rehydration
retained the physical flocculation and
settling properties of the viable biomass
and appeared to have a long shelf life.
  Stripping, sorptive,  and bio-oxidative
fates of the test chemical of interest were
determined for batch, fill-and-draw, and
continuous laboratory-scale activated
sludge (LAS) reactor conditions. Conven-
tional analytical techniques using chro-
matographic procedures and radiochem-
ical tracers were used  to  determine
influent and effluent chemical concentra-
tions,  fractions of sorbed and stripped
chemicals, and biological degradation and
transformation products including CO2.

Stripping Predictive Fate
Method Results
  Stripping  tests were conducted with
experimental equipment  as  shown  in
Figure 1. The system's liquid volume was
about 26  L, and air flows from 2 to 8
L/min were used.  The stripping  PFM
developed offers a simpler approach for
estimating stripping rates in clean water
and wastewater than other approaches
based on  the two-film theory of mass
transfer. This method incorporates the
Henry's law constant (Hc in torr  L/g-
mole) and the liquid volume-to-air flow
ratio (V/Qair) to directly yield the stripping
rate constant  Kasta) for  clean water
systems. Equations  predicting the strip-
ping rate  constant from the compound
Henry's law constant follow the form of
Ka sta • V/Qa,r = 3.71 x 1CT3 (Hc)1 °45 for a
clean water system. Units  are hr~1 for Ka
sta and hr for V/Qa,,. When the dimen-
sionless Henry's law constant(Hi) is used,
the dimension less equation, Ka8VV/QaiI
= H,, is developed. This result, along with
other studies in this area,  strongly sug-
gest that the process of stripping  from
coarse  bubble diffuser  systems  is a
single-stage equilibrium process.
  The presence of surfactants, salts, oils,
and nonviable biomass was found to vary
the stripping rate, but in no case was the
effect more  than 50% when compared
with that  of clean water. The effect
seemed to be the strongest for the higher
volatility compounds.
  The values of the stripping rate  con-
stant, Ka sta, predicted from the model
developed in this study, seem  to agree
reasonably well with previously reported
values. This suggests the  possibility of
application beyond the compounds stud-
ied herein.
  The stripping PFM was tested in  con-
tinuous LAS  units. The measured toluene
stripping rate was found to be consistent
with the predicted toluene  stripping rate
constant. This further substantiates that
the stripping PFM  may be useful for
prediction  of compound stripping in con-
tinuous "real world" systems.


Biomass Sorption Predictive
Fate Method Results
  Sorption experiments were conducted
to determine sorption kinetic rate con-
stants and equilibrium relationships be-
tween aqueous phase concentration and
loadings onto biological solids for three
test compounds. Test compounds were
chosen to span a wide range in potential
for sorption  as  indicated by the octanol-
water  partition coefficient (Kow). Com-
pounds that were studied include phenol
(Kow = 31),  1,4-dichlorobenzene (Kow =
2455), and pentachlorophenol (associated
form, Kow  = 132,000; dissociated form at
pH = 7, Kow = 7,700). All  octanol-water

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partition coefficients in this summary are
unitless ratios of equilibrium compound
concentrations in the octanol and water
phases.
  Tests with phenol and 1,4-dichloro-
benzene indicate that  equilibrium  was
reached in less than 15 minutes. Penta-
chlorophenolsorption appears to follow a
two-step process, with a very rapid initial
sorption step and subsequent slower
approach to equilibrium.
  For batch testing where sorption is the
sole removal mechanism, the equilibrium
aqueous concentration and substrate
loading on biomass may be expressed:
Cae =
       (K0*XfL/1000pL)+1
 C,   =
where:

Cae - equilibrium aqueous phase sub-
      strate concentration (//g/L)
Cs  = solids loading on biomass (yug/g)
Cao = initial aqueous phase  substrate
      concentration (//g/L)
Kow = unitless concentration ratio octa-
      nol/water partition coefficient
X   = solids (biomass) concentration
      (mg/L, dry basis)
fL   = lipid weight fraction of biomass
PL  = lipid density (g/L)
  Table 1 presents a summary  of the
measured and predicted endpoint (equil-
ibrium)  values  of Cae for the sorption
experiments. Table 2 presents  measured
and  predicted percent  removals  calcu-
lated from data in Table 1 and the starting
concentrations. Table 3 presents meas-
ured and predicted loadings (Cs).
  Generally, good agreement is seen
between measured and predicted values.
Exceptions occur for experiments SP-1
and 2, the start-up experiments, and SP-6
where the mixing intensity was reduced
and the experiment was run at 4°C.
Bio-oxidation Kinetic
Measurements
  The contribution  of  bio-oxidation to
predictive fate  assessment of organic
pollutants in industrial waste  treatment
was determined for batch, fill-and-draw,
and  continuous LAS  bioreactors.  Bio-
oxidation of specific pollutants was meas-
         Wat er In
                                                              To Gas
      Nitrogen In
                                                       Sampling System
                                                      (Figures 5, 6, and 7)
              Symbols

      PR—Pressure Reducer
       R—Regulator
      FE—Rotameter
      TE— Thermometer
       D—Drain
      SP—Sample Port
     PSV—Pressure Relief Valve
      DO—Dissolved Oxygen Probe
       PI—Pressure Indicator
 Air In
Dew Point
Hygrometer
                                        Manometer
Figure 1.    Apparatus Used in the Stripping Experiments
ured in activated sludge samples under
batch assay conditions.  Mineralization
(oxidation to C02) of 14C-labeled pollutants
was chosen as a primary and unambig-
uous measurement of bio-oxidation.
  Qualitative and quantitative measure-
ments  of specific degradative bacterial
populations comprising  the activated
sludge were performed. These measure-
ments and associated enzymatic activites
were used to evaluate the potential for
describing bio-oxidation  kinetics as a
function of the biological  community. In
addition, the potential for predicting qual-
itative  and  quantitative  pollutant  fate
relative to sludge composition and activity
was investigated.
                Laboratory-Scale Activated
                Sludge Study

                  The  purpose of  this study  was  to
                quantify the removal mechanisms of four
                organic substrates in continuous flow,
                completely mixed activated sludge units.
                Two 11-L LAS units were operated  at
                mean cell  residence times of approxi-
                mately 5 and 10 days. These data were to
                be used to test the predictive fate methods
                that had  previously been developed for
                stripping, sorption, and bio-oxidation.
                  Material balances around the activated
                sludge units  revealed that the  fate  of
                phenol and aniline are almost identical,
                with >99.8% of the parent compound bio-

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Table  1.    Comparison of Measured and Predicted Sorption Endpoint Concentrations for Batch
           Experiments
                                     Measured       Predicted
                                    Concentration   Concentration'     Percent"
      Compound	Experiment	  (mg/L)	fmg/L)         Deviation
Phenol SP-3
SP-4
SP-5
SP-6
1,4-Dichlorobenzene SP-1
SP-2
SP-10
SP-11
Pentachlorophenof SP-7
SP-8
SP-9
SP-11
73.0
73.3
71.8
76.8
26.6
54.2
13.9
2.7
0.8
1.5
0.3
0.7
74.2
74.6
72.8
75.7
17.8
33.8
14.3
3.5
0.91
1.22
0.78
0.99
-1.6
-1.8
-1.4
1.4
33.0
37.6
2.9
-29.6
-13.8
18.7
-160
-41.4
"Where fL - 0.2 and PL = 900 g/L.
"Percent deviation = (measured value - predicted value) -f- measured value x 100.
cPentachlorophenol partially ionized at pH = 7, Kow = 7700.

Table 2.    Comparison of Measured and Predicted Sorption Percent Removal
Compound
Phenol



1 ,4 -Dichlorobenze ne



Pentachlorophenof



Experiment
SP-3
SP-4
SP-S
SP-6
SP-1
SP-2
SP-10
SP-11
SP-7
SP-8
SP-9
SP-11
Measured
Removal f%)
4.6
5.8
3.9
1.3
43.0
30.0
72.7
78.7
86.9
76.9
97.2
92.2
Predicted
Removal* (%)
3.0
4.1
2.5
2.7
61.9
56.4
72.0
72.4
85.1
81.2
92.7
89.0
Difference"
(%)
1.6
1.7
1.4
-1.4
-18.9
-26.4
0.7
6.3
1.8
-4.3
4.5
3.2
"(initial concentration - endpoint concentration) 4- initial concentration x 100.
"Difference = measured removal - predicted removal.
cPentachlorophenol partially ionized at pH = 7. /fow = 77OO.
 Table 3.    Comparison of Measured and Predicted Loading for Sorption Batch Experiments
Compound Experiment
Phenol SP-3
SP-4
SP-5
SP-6
1,4 -Dichlorobenzene SP- 1
SP-2
SP-10
SP-11
PentachlorophenoP SP-7
SP-8
SP-9
SP-11
Measured
Loading
(mg/g)
0.8
0.7
0.8
0.3
6.7
9.8
7.9
2.7
1.6
2.0
1.4
1.7
Predicted
Loading'
(mg/g)
0.5
0.5
0.5
0.5
9.7
18.4
7.8
1.9
1.6
2.1
1.3
1.7
Percent
Deviation
37.5
28.6
37.5
-66.7
-44.8
-87.8
1.3
29.6
1.9
-4.0
5.0
0.6
 *C, Values
 "Pentachlorophenol partially ionized at pH = 7, /Cow = 7700.
oxidized and stripping  losses below de-
tectable limits. Approximately 56% of the
feed 14C phenol was recovered as 14COz
for both compounds. Removal of these
compounds from activated sludge  units
by sorption is insignificant on a material
balance basis, with  average compound
loadings of <84 /ug/g MLSS and 28 /ug/g
MLSS determined for phenol and aniline,
respectively.
  Biological oxidation  was  also deter-
mined to be the major removal mechan-
ism for the toluene, the most volatile of
the test compounds. Approximately 67%
to 70% of  the  feed toluene 14C was
recovered as 14CO2 and only 5% to 6% of
the 14C was recovered as soluble metabo-
lites. The  ability of the activated sludge
systems to biologically degrade toluene
was found to be very sensitive to devia-
tions from steady-state operating condi-
tions (flow fluctuations, etc.). Grab  sam-
ples of mixed liquor indicated variations
in the concentration of toluene in the
aqueous phase to range from <0.05 mg/L
to 4.7 mg/L.
  Pentachlorophenol was found  to be
extremely resistantto biological oxidation
and stripping. Sorption onto sludge was
determined to be the major removal
mechanism, with both  14C analyses and
Pentachlorophenol  analysis indicating
that 6% to 8% of the feed pentachloro-
phenol was removed through sorption to
waste solids. The average pentachloro-
phenol loading on biological solids was
determined to be 1967 pg/g MLSS and
1801  ug/g  MLSS for reactors 1 and 2,
respectively.
  The predictive fate method, which was
developed for stripping, was determined
to be accurate in predicting  the concen-
tration of test compounds in the vent gas
as  a function of the measured concen-
tration in the aqueous phase, the Henry's
law constant, and the  relative air flow/
liquid volume ratio. Vent gas concentra-
tions of toluene predicted  from  daily
average data were within ±50% of ob-
served values for approximately 70% of
the observations. The remaining observa-
tions had either or both vent gas and/or
mixed liquor concentrations below the
detection  limit.
  Average loading of aniline, phenol, and
Pentachlorophenol onto biological solids
were found to be related to the octanol-
water partition coefficient. However, the
proposed  predictive equation for relating
equilibrium loading  to the equilibrium
aqueous phase concentration was found
to predict loadings that were lower than
those observed for aniline,  an ionizable

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compound. Conversely, predicted penta-
chlorophenol loadings were seven-fold
higher than those observed.
Overall Mathematical Predictive
Fate Method
  An  overall mathematical PFM  was
developed  to  predict the  equilibrium
aqueous phase  concentration in the
secondary  effluent  from a  completely
mixed activated sludge system. The strip-
ping PFM and the equilibrium sorption
PFM for substrates at low concentrations
are incorporated into traditional "uniform
biomass" design  models  taken  from
environmental engineering.  This equa-
tion, and its derivation,  is given in the
project report.

Conclusions
  This work represents a broad overview
assessing the feasibility of  using  both
experimental and mathematical predic-
tors to  quantitatively  determine fates.
Methodology using chemical engineering
kinetic  approaches  and  reactor-design
equations appears to be a viable way to
analyze multi-mechanism processes for
various  reactor configurations.
  The data base existing at the beginning
of this effort was limited because of the
specific emphasis given to different ques-
tions in  each study and to the past focus
on removal as opposed to specific chem-
ical fates. Some indications on relative
fate processes may still be drawn, partic-
ularly from more recent studies that look
at numerous compounds with the  same
experimental protocol.
  Stripping in completely mixed, diffused
air systems has been found to be essen-
tially an equilibrium process, and predic-
tive equations are proposed. Verification
on other compounds and system config-
urations is  suggested.  The effects  of
contaminants(surfactants, salts, oils, and
nonviable biomass) are  significant on
oxygen transfer rate constants and less
significant on stripping transfer process-
es.  Stripping rate estimates based on
oxygen  transfer rates  for contaminated
waters  such as treatment  plant mixed
liquors must be questioned.
  Sorption was quantified in a variable-
volume  batch reactor using nonviable
biomass and later in continuous labor-
atory activated sludge  studies. An equil-
ibrium deterministic predictive equation
is proposed for low aqueous concentra-
tions.  Kinetic sorption rates for the com-
pounds  studied could  not be quantified
because of their rapidity compared "with
the time required for sampling and anal-
ysis.
  Numerous  kinetic rate constants for
biological  processes exist and can be
formulated. Each of these rates applies to
specific cases in substrate and biomass
concentration and reactor configuration.
Little reliable data exist in this area, and
accepted overall methodologies are lack-
ing. First- and second-order (first order in
both substrate  and  biomass concentra-
tion) rate constants are developed in this
study for batch, fill-and-draw, and contin-
uous reactor configurations for the com-
pounds studied.  Disappearance  rates
were calculated, but mineralization rates
were emphasized.  Mineralization  pro-
vides an unambiguous predictor of bio-
degradation, but disappearance kinetics
are required for fate predictive equations.
Mineralization rates for the compounds
studied were generally comparable over
the batch, fill-and-draw, and continuous
reactor configurations. However, disap-
pearance rate kinetics were comparable
only for batch and fill-and-draw systems
and ranged from 2 to 3 orders of magni-
tude slower than those demonstrated in
the steady-state continuous systems. The
batch  and fill-and-draw kinetic disap-
pearance values are of the same order as
data reported in the literature for specific
compounds and BOD.
  Laboratory-scale activated sludge sys-
tems were  designed and  operated  to
elucidate compound fates in a conclusive
fashion. This included the use of radio-
labeled substrate  in  conjunction  with
nonlabeled substrate and sampling of all
streams of fate importance. Many of these
procedures are substantially more  diffi-
cult to implement in full-scale processes.
Full-scale  fate data cannot, therefore, be
as precise or conclusive as  the  more
controlled experiments.
  A  coupled, algebraic, predictive fate
equation is presented subject to assump-
tions and derivations given in the project
report. An example of organic compound
fates is  provided  by  assuming  most
probable, maximum, and minimum values
for  the equation variables  and  using
biological rate constants calculated from
other studies. Generally, the most prob-
able values agree with the findings in this
study,  and the ranges agree with full-
scale plant studies implemented by  EPA.
  The full report was submitted in fulfill-
ment of Contracts No. 68-03-3027 and
68-03-3074 by IT Corporation and the
University of  Tennessee (subcontract)
under the  sponsorship of the U.S.  Envi-
ronmental Protection Agency.
                                                                               U. S. GOVERNMENT PRINTING OfFICE: 1985/646-116/20718

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    J. W. Blackburn, W. L. Troxler, K. N. Truong, R. P. Zink. S. C. Meckstroth, J. R.
      Florence, and A. Groen are with IT Corporation, Knoxville,  TN 37923; G. S.
      Sayler, R. W. Beck, R. A. Mi near, and A. Breen are with University of Tennessee,
      Knoxville, TN 37916; and O. Yagi is with National Institute for Environmental
      Studies, Yatabe, Japan.
    R. J. Turner is the EPA Project Officer (see below).
    The complete report, entitled "Organic Chemical Fate Prediction in Activated
      Sludge Treatment Processes," (Order No. PB 85-247 674; Cost: $28.95, subject
      to change) will be available only from:
           National Technical Information Service
           5285 Port Royal Road
           Springfield, VA 22161
           Telephone: 703-487-4650
    The EPA Project Officer can be contacted at:
           Water Engineering Research Laboratory
           U.S. Environmental Protection Agency
           Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use S300

EPA/600/S2-85/102
           0000329   PS

           U  S  FNVIR  PROTECTION  AGENCY
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